The invention relates to a method for producing a camshaft module and a camshaft module. The camshaft module includes at least one camshaft and a bearing frame having bearing devices. The camshaft comprises at least one shaft and cams having cut-outs. The cut-outs likewise comprise the bearing devices.
Camshafts generally comprise a carrier element (also referred to as a pipe or shaft) and cams. It is also possible for additional functional elements such as bearing rings, angle transmitters or gears to be provided. When used in engines, the camshafts serve as part of the valve train, wherein the carrier element rotates about the longitudinal axis thereof. As a result of the cams, the rotational movement is converted into longitudinal movements so as to control the intake and exhaust valves of the engine.
A number of variants of camshafts, of the components thereof or of the production method are already known in the prior art. In the case of what are known as composite camshafts, the cams and other functional elements are produced separately and applied to the shaft.
The camshafts are typically applied to the cylinder head of the respective internal combustion engine by way of bearing points and attached there after production. For this purpose, the camshafts must be aligned with the cylinder head and with each other. For the bearing arrangement, split bearings are therefore required, for example, so as to be able to place the shaft in these bearings. As an alternative, the bearings, or bearing components, are already applied during production of the camshaft to the respective camshaft, in addition to the cams and remaining functional elements.
So as to simplify the production of engines, in some instances camshaft modules are used, which accommodate in particular two camshafts in corresponding bearings and are applied to the cylinder head as one unit during the actual assembly of the engines.
In a further development step, in the prior art the methods of manufacturing the camshaft are in some cases combined with the manufacture of the camshaft module. As a result, the camshafts are no longer produced individually and then introduced in the respective module, but the camshafts are produced within the module. Appropriate adjustments and adaptations must be made to the camshaft or the module based on the general circumstances (such as the shape of the module due to the design of the cylinder-head cover, space constraints, materials used).
German Patent Document No. DE 10 2010 048 225 A1 describes a method for producing camshafts, wherein a shaft is pushed through cut-outs of the individual functional elements (such as cams), and a press fit is obtained in each case by the design of the shaft and of the functional elements. During introduction of the shaft, the functional elements are held by holding elements, which in turn are disposed inside a frame. Sensors are located in the holding elements, which measure the force that is exerted by the shaft on the functional elements during production. Based on these measured values, it is possible to determine the level of torque that can be transmitted via the connection between the functional element and the shaft. In other words: by way of the force with which the shaft acts on the cams, it is possible to calculate, for example proceeding from reference measurements, how rigid the connections are, ensuring they can transmit torque up to a certain limit value without the connection detaching.
German Patent Document No. DE 10 2010 021 904 A1 describes the production of a composite camshaft, wherein the shaft has differing outside diameters. During production, the shaft is pushed through the functional elements that are disposed behind one another. A cover between sections of the shafts and the continuous cut-outs of the functional elements achieves smoothened sections of the shaft.
German Patent Document No. DE 197 10 847 C2 discloses a composite camshaft, during the production of which the separately produced cams are applied to receiving projections of a shaft. The outside diameters of the receiving projections become smaller in a direction of the shaft. For attachment of the cams, the inside cut-outs thereof or the receiving projections have axial teeth, which generate a connection between the cam and the shaft in each case in a chip-removing manner when the cams are applied to the shaft.
German Patent Document No. DE 10 2008 007 091 B4 describes a camshaft module, in which two produced camshafts are rigidly connected to a cylinder-head cover by way of bearing brackets.
German Patent Document No. DE 10 2009 051 636 A1 describes a production of a camshaft module, in which the camshafts are produced within the module. For this purpose, in one step the individual functional elements are threaded with the respective associated tolerance ring on the shaft. Subsequently, an axial relative movement between the tolerance ring and the functional element generates an interference fit between the functional element, tolerance ring and shaft.
The essential aspect during production is that the orientation of the camshafts with respect to each other and the orientation of the cams within the individual camshaft is not changed by the production process. The orientation of the cams with respect to each other is essential for valve timing when the module is installed.
A particular problem area frequently results from the gears, by way of which the camshafts are rotated, and the axial bearings, which define the support region of the camshaft module on the engine block. The problem here arises from the fact that the shafts can be easily deformed by the cams, by other functional elements, bearings or the like as a result of the force that occurs when it is pushed through, whereby fluctuations in the axial distances of the components with respect to each other can occur. The gears are typically disposed so as to abut a bearing bracket. The distance between an axial bearing and the gear must not be too small, however, because otherwise the unobstructed rotation of the gear, and thus of the camshaft, could be impeded.
It is therefore the object of the invention to provide a production method for a camshaft module, which allows high manufacturing accuracy and small dimensional deviations, wherein in particular the occurrence of interfering forces during and after production in the camshaft module is prevented.
The method according to the invention, in which the above-derived and above-described object is achieved, is initially and essentially characterized in that the shaft is created and/or machined in such a way that the shaft has at least two different outside diameters, at least some of the cams and/or some of the bearing devices are created and/or machined in such a way that the cut-outs of the cams and/or the cut-outs of the bearing devices have differing diameters, the bearing frame is held in such a way that the bearing frame, during production of the camshaft module, is movable along at least one movement axis and substantially rigid along an insertion direction of the shaft, the cams are disposed relative to the bearing frame in such a way that the cams—in particular by the elevations thereof—are aligned with each other, and the diameters of the cut-outs of the cams and the diameters of the cut-outs of the bearing devices become smaller in the insertion direction, and the shaft is inserted in the insertion direction into the bearing frame at least through the cut-outs of the cams and the cut-outs of the bearing devices in such a way that the outside diameter of the shaft increases against the insertion direction, and a respective interference fit is obtained in each case at least between the shaft and at least some of the cams. In one embodiment, all cams are attached to the shaft by way of interference fit. In one embodiment, an interference fit is also generated between the shaft and at least some of the bearing devices.
According to the invention, the bearing frame, which in particular allows installation on the engine block, is at least partially floatingly mounted, which is to say it can give way to a certain degree, which is determined by the elements used for mounting, as a result of the forces acting on the bearing frame. For this purpose, spring elements, which allow a movement and subsequently act in a restoring manner, are preferably provided in the devices for mounting the bearing frame. The functional elements—such as cams—and other bearing devices—such as bearing rings or bearing brackets—are either part of the bearing frame, or are disposed in the same for production in such a way that they move together with the same. As an alternative, elements are also held separately from the bearing frame, however they are disposed so as to assume their final position already inside the camshaft module. By way of the floating bearing arrangement, self-centering of the bearing frame can be achieved as a result of the movement of the shaft, so that in particular damaging forces or stresses or the like are avoided. For example, some of the bearing devices comprise rolling bearings or rolling bodies, which preferably should not be subjected to any axial or radial forces during production. The floating bearing arrangement thus allows the configuration to give way.
The shaft moreover has a stepped design, wherein the components (such as cams, bearing rings, the bearing devices in general, or the functional elements in general), through the cut-outs of which the shaft is guided during production, are provided with matching inside diameters of the cut-outs thereof. Due to the stepped design of the shaft and the arrangement of the components corresponding to the diameters of the cut-outs, the shaft can be inserted up to a certain preliminary position, without any force being exerted on the components surrounding the shaft. A force action does not occur initially since the shaft is introduced with the smallest diameter facing forward, and the diameters of the cut-outs decrease in the movement direction, so that the shaft is first guided through the larger inside diameters. A clearance thus essentially exists between the shaft and the functional elements (such as cams) or the bearing devices (such as bearing rings, bearing brackets) on those components that are not joined to each other, and an interference fit results for the components that are to be joined to each other. In one embodiment, multiple functional elements or cams and/or bearing devices following one another in the arrangement in the bearing frame are thus provided with the same inside diameter of the cut-outs. As a result, not all inside diameters of the cut-outs must differ; for the method according to the invention they only have to be located in a such way, relative to the bearing frame, that it is possible to guide the shaft through all components.
In one variant, the components forming the camshaft module, which is to say in particular the cams and bearing rings, for example, are already completely machined prior to installation. The bearing rings or bearing brackets are in particular also fully closed components, through the continuous cut-outs of which the shaft is pushed and subsequently secured, preferably by way of interference fit.
In one embodiment, the shaft is provided with a knurling at least in some regions.
In one variant, two camshafts are introduced next to each other into the module. Two camshafts are used, for example, for intake and exhaust valve timing.
One embodiment of the method provides for the bearing frame to be created with at least some of the bearing devices. As an alternative or in addition, at least some of the bearing devices are disposed relative to the bearing frame after separate production. The bearing devices are in part bearing rings—such as rolling element bearings—or larger elements, such as bearing brackets. Some of these are integral parts of the bearing frame or are disposed relative to the bearing frame for production.
According to one embodiment, the method is carried out substantially at room temperature. As an alternative or in addition, at least the insertion of the shaft is carried out at a temperature that is substantially identical for the bearing frame and camshaft. In the prior art, individual components are heated, while others are cooled. This complexity is not required with the method according to the invention. Moreover, as an alternative or in addition, the insertion of the shaft is additionally carried out free of a locking agent.
In one embodiment, the force that is applied to the shaft during insertion of the shaft is measured. By monitoring the applied force, the interference fit that is created can be inferred, by way of which the maximal torque can be determined which can be transmitted via the connection—for example between the cams and the shaft.
According to one embodiment, the bearing devices and the cams are fully rough-machined elements, which are designed to be substantially closed around the respective cut-outs. No secondary machining is therefore required, and the production method differs from some of the prior art in particular by the shaft being guided through the cut-outs of the components that are already closed.
To supplement the embodiments of the above-described method, it is also possible to carry out and implement the steps described hereafter. However, the following method also allows a camshaft to be produced without the steps of the method described above. Accordingly it is optionally sufficient for the following method if the camshaft module comprises at least one camshaft that has at least one shaft and cams. The remaining components described above are not absolutely necessary for implementing the following method, but also do not adversely conflict with an implementation of the method. However, individual of the above-mentioned embodiments can also be implemented in the following method.
As an alternative or in addition, the object described above is achieved in a further teaching of the invention by the following method, which consists of partially inserting the shaft in the cut-out of a functional element, determining at least a distance between the functional element and a reference element, comparing the determined distance to a predefinable target distance and generating a comparison result, and exerting a force on the shaft based on the comparison result. The force is in particular such that it causes the shaft to be pushed further into the cut-outs of the functional element or through the same.
So as to optimally achieve the distance between the functional element and the reference element according to the second teaching of the invention, the shaft is initially introduced only partially into the cut-out of the functional element, wherein already a certain tension is created. The certain functional element is in particular the last component, through the cut-out of which the shaft is pushed. In one embodiment, the functional element is thus located opposite the region on which the shaft is inserted into the bearing frame. The insertion of the shaft into the cut-out of the functional element already causes a certain force to act. After insertion, the movement of the shaft is stopped, and a distance between the functional element and a reference element is measured and compared to a target value. Starting from the resulting comparison result, which is to say in particular starting from the difference between the measured value and the target value, a force is then exerted on the shaft, which brings the shaft to the final position, so that in particular the distance between the functional element and the reference element corresponds to the target value.
The above-described method can be employed for a specific functional element, or also for further functional elements, cams or bearing devices of the camshaft or of the camshaft module. The method can thus also be employed separately from the above-described method, or be used to supplement the same.
According to one embodiment, the distance is determined while the shaft and/or the functional element are free of a force that is exerted on the shaft or on the functional element. Thus, no force from the outside acts during the time during which the distance is measured or determined; only the force that has already built between the shaft and the functional element is the one that acts.
In a further embodiment, the shaft is partially inserted into the cut-out of the functional element in such a way that the distance between the functional element and the reference element is greater than the predefinable target distance. In this embodiment, the movement of the shaft causes the distance between the functional element and the reference element to be reduced, whereby the movement of the shaft is stopped at the moment at which further action of a force would further reduce the distance. If, as an alternative, the movement causes the distance to become larger, the movement of the shaft would be interrupted at the moment at which it is to be expected that the distance is smaller than the target distance.
According to one embodiment, the functional element is a gear and the reference element is an axial bearing.
Finally, the invention relates to a camshaft module that has been produced according to at least one of the above-described embodiments.